"unknown" type testing doesn't work in unreachable code.

[mpawelski]

Bug Report

🔎 Search Terms

unknown allowUnreachableCode

🕗 Version & Regression Information

4.5.4 and 4.6.0-dev.20220107

⏯ Playground Link

Playground link with relevant code

💻 Code

function errorHandler2(error:unknown){
  return;
  if(error instanceof Error){
    console.log(error.message); //Error: Object is of type 'unknown'.
  }
}

function errorHandler3(error:unknown){
  throw error
  if(error instanceof Error){
    console.log(error.message); //Error: Object is of type 'unknown'.
  }
}

🙁 Actual behavior

I've put return or throw statement just for debugging purpose to end function earlier. And I got compiler error in later code.

🙂 Expected behavior

No error because I have allowUnreachableCode: true in tsconfig (default) and the unreachable code is valid (but compiler says it is not).

Small bug IMO, nothing serious, but it's something I didn't expect.

[MartinJohns]

Duplicate of #26914.

allowUnreachableCode causes unreachable code itself to not error. But due to the linked bug the type checking does not work as expected within unreachable code, resulting in a type error.

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.